Bromination of organic compounds with a bromine chloride dioxane complex

ABSTRACT

A BROMINE CHLORIDE COMPLEX OF P-DIOXANE HAS BEEN DISCOVERED WHICH IS USEFUL AS A SOLID SOURCE OF BROMINE CHLORIDE. A DIOXANE-BROMINE CHLORIDE COMPLEX FORMED BY MIXING BROMINE CHLORIDE WITH DIOXANE IN METHYLENE CHLORIDE AT 10*C. HAS BEEN USED TO SELECTIVELY BROMINATE SALICYLANILIDE TO GIVE AN 88% YIELD OF 3,4&#39;&#39;,5-TRIBROMOSALICYLANILIDE.

United States Patent US. Cl. 260559 S 1 Claim ABSTRACT OF THE DISCLOSURE A bromine chloride complex of p-dioxane has been discovered which is useful as a solid source of bromine chloride. A dioxane-bromine chloride complex formed by mixing bromine chloride with dioxane in methylene chloride at C. has been used to selectively brominate salicylanilide to give an 88% yield of 3,4',5-tribromosalicylanilide.

CROSS-REFERENCE TO OTHER APPLICATION This application is a division of copending parent application Ser. No. 819,541, filed Apr. 24, 1969, now Pat. No. 3,607,883.

BACKGROUND OF THE INVENTION Various complexes of bromine with diiferent compounds are shown by Z. E. Iolles in his book entitled Bromine and Its Compounds, published by the Academic Press, New York, 1966 beginning at page 368.

SUMMARY OF THE INVENTION According to the invention, an equimolar complex of p-dioxane and bromine chloride has been discovered which is useful as a selective brominating agent. The complex of the invention is easily prepared by mixing essentially equimolar amounts of p-dioxane and bromine chloride in the presence of a suitable solvent. Upon evaporation of the solvent, the bromine chloride complex remains as a relatively stable solid. Optionally, instead of evaporating the solvent, the bromine chloride complex may be used in the reaction solution.

The concentrations of the bromine chloride and pdioxane in the reaction to form the complex may vary widely. The ratio of dioxane to bromine chloride may suitably range from about 0.9 to about 20 or more. The ratio is not critical, but an excess of either reactant is generally used to assure complete formation of the complex.

The bromine chloride of the present invention may suitably be introduced from the liquid bromine chloride prepared in a closed container by adding equal molar amounts of bromine and chlorine. By employing this technique, an essentailly constant composition mixture of bro mine chloride, with minor amounts of chlorine and bromine is introduced into the reaction chamber.

The solvent of the present invention may suitably be any organic solvent in which the reactants and products are at least partially soluble. If the solid complex is desired, a solvent that is easily separated should be used. Among the preferred solvents of the invention are the easily vaporized lower chlorinated solvents such as the methylene chloride, chloroform, carbon tetrachloride and ethylene dichloride and the lower alkyl ethers such as dimethyl and diethyl ether.

3,755,444 Patented Aug. 28, 1973 ice The reaction to form the complex may be suitably conducted over a wide range of temperatures, for example about 0 to about C. or more. Because of the volatility and toxicity of the bromine chloride, however, the complexing reaction is preferably conducted at a temperature below 40 C.

After the complexing reaction has been completed, the solvent is evaporated and a solid reaction product is formed. The complex formed melts at 45-55 C. and is unstable over an extended period of time because of the slow evolution of bromine chloride.

The greatest advantage of the bromine chloride complex formed in the present invention is the fact that the complex is a ready source of bromine chloride having a low vapor pressure. This is distinguished from neat bromine chloride. When the bromine chloride is used without complexing, the high vapor pressure and toxicity of the bromine chloride vapors makes handling diflicult and dangerous.

Another surprising feature of the invention is the ability of the bromine chloride complexes to selectively brominate organic compounds. With the complex, a narrower range of isomers in a bromination reaction is obtained. In addition, the complex is a milder brominating agent than bromine chloride as such.

SPECIFIC EMBODIMENTS Example 1 A dioxane-bromine chloride complex was prepared at a temperature of 10 C. by adding dropwise 35.2 g. (0.4 mole) of 1,4-dioxane to a solution of 49 g. (0.42 mole) of bromine chloride in 100 ml. of methylene chloride. The methylene chloride was removed under reduced pressure, and 60.5 g. of an orange solid melting at 45 55 C. was obtained. Based on the dioxane used in the reaction the orange solid was 74% of the theoretical yield.

Example 2 The specificity of the p-dioxane-bromine chloride complex of Example 1 as compared to the use of bromine chloride and bromine was analyzed by the bromination of salicylanilide. The object of the bromination was to maximize the yield of the tribromo compound. The comparative results of the tests of dioxane-bromine chloride complex, bromine chloride and bromine all in methylene chloride are summarized in Table I.

TABLE I A comparison in the use of a dioxane-BrCl complex, BrCl and Br; to prepare 3,4,5-tribromosalicylanilide from salicylanilide p-Dioxanel Room temperature. 2 Dioxaue solvent. 3 Methylene chloride solvent.

In the same manner as described above, the complex of Example 1 may also be used to selectively brominate other polybrominatable compounds such as bisphenol, benzene,p-xylene and the like to make tetrabromobisphen01, mono and dibromobenzene and monobromo-p-xylene.

3 4 We claim: References Cited 1. A method of bromiating an organic compound se- R. Kosolapofig; Am m Soc, ,vol 75 3 597.

lected from the group consisting of salicylanilide, bis- 97 (1953),

phenol, benzene, and p-xylene, comprising reacting by contacting the organic compound with a complex of p- 5 HARRY Pnmary Examiner dioxane with bromine chloride at a temperature in the US, Cl. X R, range of 0 to 20 C., and in inert organic solvent. 260620; 650 R 

